1. Field of the Invention
The present invention relates to a control device for a vehicle and a method of controlling a vehicle that enable a vehicle to travel through inertia by blocking power transmission between an engine and drive wheels.
2. Description of the Related Art
A vehicle that carries out a control related this type of travelling through inertia is conventionally known. In such control, a power connecting/disconnecting device between an engine and drive wheels is released to block the power transmission between the engine and the drive wheels during the travelling, as in the techniques disclosed in Japanese Patent Application Laid-open No. 2012-030710 and International Publication Pamphlet No. WO 2013/030920, for example. In the technique disclosed in Japanese Patent Application Laid-open No. 2012-030710, a clutch serving as a power connecting/disconnecting device is released to start the traveling through inertia when an output torque of the engine enters a negative region while the accelerator opening is reducing. In the technique disclosed in International Publication Pamphlet No. WO 2013/030920, fuel efficiency is enhanced by releasing the clutch serving as the power connecting/disconnecting device to carry out the traveling through inertia not only when the accelerator opening is fully closed but also when the accelerator opening is equal to or smaller than a predetermined opening. Furthermore, in the technique disclosed in International Publication Pamphlet No. WO 2013/030920, the travelling through inertia can be carried out even when a constant-speed travelling can be performed.
In this type of technique, the travelling through inertia is terminated under a predetermined condition, and the power connecting/disconnecting device is engaged to return to a normal travelling. For example, in the technique disclosed in Japanese Patent Application Laid-open No. 2012-030710, when the accelerator opening becomes equal to or smaller than a threshold value (value assumed as fully closed) during the traveling through inertia, the travelling through inertia is terminated and the clutch is engaged so that the engine brake can be actuated. Thus, when the accelerator opening is fully closed during the traveling through inertia, the vehicle deceleration rapidly increases from the vehicle deceleration during the traveling through inertia to the vehicle deceleration by the engine brake, and such difference in the levels of the vehicle deceleration may give a sense of discomfort to the driver. To solve this problem, the difference in the levels of the vehicle deceleration can be made smaller by slidably engaging the clutch in returning to the normal travelling. However, such a measure against the difference may lower the durability of the clutch.
There is a need for a control device for a vehicle and a method of controlling a vehicle that can suppress the fluctuation of the vehicle deceleration while avoiding the lowering of the durability of the power connecting/disconnecting device.